Scanning probe system

Abstract

A method of scanning a sample with a scanning probe system, the scanning probe system comprising a probe comprising a cantilever extending from a base to a free end, and a probe tip carried by the free end of the cantilever, the method comprising using the probe to measure an electrostatic interaction between the sample and the probe; and after measuring the electrostatic interaction between the sample and the probe, scanning the sample with the probe while simultaneously applying a bias voltage to the scanning probe system, the applied bias voltage based on the measured electrostatic interaction between the sample and the probe.

The invention claimed is: 
     
       1. A method of scanning a sample with a scanning probe system, the scanning probe system comprising a probe comprising a cantilever extending from a base to a free end, and a probe tip carried by the free end of the cantilever, the method comprising:
 moving the probe to a measurement position at which the sample imposes an electrostatic force on the probe; 
 at the measurement position: applying a measurement voltage to the scanning probe system, varying the measurement voltage applied to the scanning probe system, and monitoring a reaction of the probe to the variation of the measurement voltage to measure a counteracting voltage value which reduces or nullifies the electrostatic force on the probe at the measurement position; and 
 after the counteracting voltage value has been measured, scanning the sample with the probe while applying a bias voltage to the scanning probe system, wherein the bias voltage is based on the counteracting voltage value. 
 
     
     
       2. The method of  claim 1 , comprising:
 moving the probe to a plurality of measurement positions at which the sample imposes an electrostatic force on the probe; and 
 at each measurement position: applying a measurement voltage to the scanning probe system, varying the measurement voltage applied to the scanning probe system, and monitoring a reaction of the probe to the variation of the measurement voltage to measure a respective counteracting voltage value which reduces or nullifies the electrostatic force on the probe at the measurement position; and 
 determining the bias voltage on the basis of at least two of the counteracting voltage values. 
 
     
     
       3. The method of  claim 2 , wherein an area of the sample is scanned with the probe, and the bias voltage is determined on the basis of a location of the area of the sample. 
     
     
       4. The method of  claim 3 , wherein the bias voltage does not vary during the scanning of the area of the sample. 
     
     
       5. The method of  claim 3 , wherein:
 a first bias voltage is determined on the basis of a location of a first area of the sample, and the first bias voltage is applied to the scanning probe system during scanning of the first area of the sample; and 
 a second bias voltage is determined on the basis of a location of a second area of the sample, and the second bias voltage is applied to the scanning probe system during scanning of the second area of the sample. 
 
     
     
       6. The method of  claim 1 , wherein the counteracting voltage value is determined at the (or each) measurement position with the probe tip spaced from the sample by a distance greater than 1 μm. 
     
     
       7. The method of  claim 1 , further comprising storing the (or each) counteracting voltage value before the sample is scanned. 
     
     
       8. The method of  claim 1 , wherein an area of the sample is scanned with the probe, and the bias voltage applied to the scanning probe system does not vary during the scanning of the area of the sample. 
     
     
       9. The method of  claim 1 , wherein scanning the sample with the probe comprises taking a series of scanning measurements of the sample at a series of scanning positions across the sample; and wherein each scanning measurement is taken by moving the probe tip towards the sample, taking a scanning measurement at a respective one of the scanning positions, then retracting the probe tip away from the sample. 
     
     
       10. The method of  claim 9 , wherein the bias voltage applied to the scanning probe system does not vary from scanning position to scanning position. 
     
     
       11. The method of  claim 9 , wherein for each scanning measurement the bias voltage applied to the scanning probe system remains substantially constant as the probe tip moves towards the sample, and as the probe tip retracts away from the sample. 
     
     
       12. The method of  claim 1 , wherein the variation of the measurement voltage causes the probe to deflect, and the deflection of the probe is monitored to determine the counteracting voltage. 
     
     
       13. The method of  claim 1 , wherein the variation of the measurement voltage causes an oscillation parameter of the probe to change, and the oscillation parameter is monitored to determine the counteracting voltage. 
     
     
       14. The method of  claim 1 , wherein the measurement voltage and the bias voltage are applied to the probe. 
     
     
       15. The method of  claim 1 , wherein the measurement voltage and the bias voltage are applied to a conductor proximate to the sample. 
     
     
       16. The method of  claim 1 , wherein scanning the sample with the probe comprises imaging the sample with the probe so as to generate an image having a plurality of pixels. 
     
     
       17. The method of  claim 16 , wherein the bias voltage applied to the scanning probe system is the same for each pixel of the image. 
     
     
       18. A scanning probe system comprising: a probe comprising a cantilever extending from a base to a free end, and a probe tip carried by the free end of the cantilever; wherein the scanning probe system is arranged to perform the method of  claim 1 . 
     
     
       19. The scanning probe system of  claim 18 , wherein the scanning probe system is arranged to apply the bias voltage to the probe. 
     
     
       20. The scanning probe system of  claim 19 , wherein the cantilever comprises an electrically conductive layer separated from the tip by an electrically insulating barrier, and the scanning probe system is arranged to apply the bias voltage to the electrically conductive layer.